The present invention relates to an apparatus for analyzing particles by passing a sample liquid containing particle components such as blood and urine in a sheath flow, and measuring the fluorescent spectra of the particles in the flow. The sample liquid is irradiated with light, signals detected from the particles, and the particles analyzed; and more particularly to an apparatus for analyzing particles capable of obtaining spectra of light signals by using spectroscopic (spectral) means such as prism and diffraction grating, thereby obtaining more specific particle information. The sheath flow is a flow having a suspension of particles the surroundings of which are covered with a laminar sheath liquid in order to align the particles in one row precisely in the middle of the liquid flow to allow passage. As the sheath liquid, usually, a diluent liquid or the like is used.
A fluorescent excitation (excited) light is irradiated to a sample liquid containing particles of dyed cells or the like, and the fluorescence emitted from the particles is detected, and the particles are classified and counted. An example of such an apparatus is a flow cytometer. Also known is an imaging flow cytometer for picking up the particle images.
In such an apparatus, when measuring the fluorescence emitted from the cells, in order to separate the desired fluorescence from other light, wavelength selection means such as an optical filter and a dichroic mirror is needed. Besides, when measuring a plurality of fluorescences differing in wavelength, a corresponding plurality of optical detectors are needed.
The Japanese Laid-open Patent Hei. 2-24535 discloses a flow cytometer capable of calculating the fluorescence intensity distribution of the wavelength of the particles to be detected, by separating the fluorescence from the specimen into consecutive wavelength components by spectroscopic means, and detecting the separated wavelength components by a one-dimensional photoelectric detector.
With an optical filter, however, it is difficult to separate the beams of light that are close in wavelength, although it is possible to separate the beams of light largely apart from each other in wavelength. In addition, the wavelength distribution of the light cannot be measured. That is, it is not possible to know the fluorescence of which wavelength is emitted from which positive of a cell by what quantity. Of course it may be possible by taking the picture of a cell image by a video camera and analyzing the image, but each cell must have a pictured image and the image processed. The apparatus thus becomes complicated.
In the apparatus for analyzing particles disclosed in the Japanese Laid-open Patent Hei. 2-24535, moreover, since the separated fluorescence is weak, it is difficult to detect the fluorescence directly by the detector. By raising (increasing) the lighting (irradiation) intensity of the light for fluorescence excitation, the fluorescence intensity may be enhanced, but the particles to be analyzed may be damaged in this case.
Besides, when using a photoelectric conversion element of the charge accumulation type such as a charge coupled device (CCD), unless the accumulated charge is reset in some way or other, the fluorescence of all the particles passing through the detection region is added up (integrated). Since the particle interval is not constant, it is necessary to detect the passing of a particle, and reset the charge on every occasion.